A common element in local neuronal circuits in the central nervous system (CNS) are dendrodendritic (D-D) synapses. Such neuron to neuron contacts have been implicated to be important in the synchronous firing and lateral inhibition of neurons, phenomena which re important for the normal functioning and pathology of many aspects of the CNS. However, very little is known about the fundamental properties of D-D synapses, which we may expect are very different from more conventional axosomatic or axodendritic synapses. Here we propose a study of the reciprocal D-D synapse between the mitral and granule cells of the rat olfactory bulb, as an example of a D-D synapse in the CNS. Whole-cell patch clamp measurements will be made from visually identified mitral and granule cells. The specific aims are: (1) to determine the membrane voltage profile at the dendritic release sites; (2) to characterize the fast and slow modulatory effects of the glutamate that is released at this synapse; and (3) to consider how the released glutamate alters the local circuit, lateral inhibitory interactions between mitral cells, which are believed to be important in olfactory sensory information processing.